Skip to main content

Full text of "Handbook Of Chemical Engineering - I"

See other formats


THE TRANSPORTATION OF LIQUIDS
123
20	24	32
78	72	51
1.073	1.372	2.418
0.657	1.096	2.136
0.416	0.276	0.282
50.450	50.300	49.400
68.700	167.350	278.150
119.150	217.650	327.550
86.200	83.800	74.400
91.200	87.000	77.200
in which q is the quantity of water raised h ft. above the source, and Q is the quantity of water wasted in falling H ft. to do the work. The efficiency under the Rankine formula is limited by the ratio of lift to fall, approximately as follows:
h/H...................     4         6         8        12       16       20       24       26
E..................... 0.72   0.61   0.52   0.37» 0.25   0.14   0.04       0
The d'Aubisson formula gives the scientific efficiency E = q(H + K) -*• (Q + q)H.
The following results were obtained by Christopher and Stramberg at the University of Washington in tests of a Hill hydraulic ram, operating under a head of 50 ft., through 140 ft. of 10-in. drive pipe:
Experiment number.......................    20
Strokes per minute........................    78
Water supply, cubic feet per second = Q -f q Water wasted, cubic feet per second = Q Water pumped, cubic feet per second = q Supply head, feet                            = H
Pumped head, feet                          = h
Delivery head, feet                          = H + h
Efficiency, Rankine, per cent...............    86.200
Efficiency, D'Aubisson, per cent.............    91.200
PUMP DETAILS
Valve Motions.—The principal features of all engine valve motions are that the valve moves while the piston is standing still (as in reversing) and vice versa. In a single direct-acting pump this is effected by having the main valve operated by an auxiliary steam cylinder with piston to which the valve is attached. A small pilot valve controlling admission to and exhaust from this cylinder is mechanically operated by the main steam piston. An example of such a valve motion is the Cameron pump, illustrated in Fig. 16. The four elements mentioned can always be recognized, although they may be combined in many ways. The Worthington duplex pump valve motion presents the same elements, but here both           Fio. 16.—Cameron valve motion,
pistons arc performing work (Fig. 2).
Crank and flywheel pumping engines equipped with Corliss releasing gear are used extensively for all services. The usual reason for using a Corliss gear is the convenient control by the fly-ball governor. This is not so necessary in a pumping engine, where the load is constant and where great sensitiveness is not needed nor desired. A fixed cutoff and hand throttle adjustment is most satisfactory in a pump which acts as a regulator in itself between certain limits.
Water Ends.—Small pumps are generally of the submerged piston or plunger type. The cap or force chamber is removable, also the discharge valve plate